Q: Why MA2.10-71xx prompts an alarm "Illegal PPPoE SERVER (FE Port x VLAN y MAC H-H-H)"?
A: MA5200F at R7 has a functionality to detect illegal PPPOE server; that is, MA5200 can emulate a user to transmit PADI packets outward actively. If some user enables PPPOE server illegally, it will echo PADO packets to MA5200. Once MA5200 receives the echo packets for PADI that are transmitted by itself, it ascertains that there is an illegal PPPOE SERVER, and prints "Illegal PPPOE SERVER(FE port x VLAN y MAC HH-HH-HH)", indicating that the illegal server locates at VLAN y of x port, with MAC as HH-HH-HH.
The disadvantages for PPPOE SERVER: if there are multiple PPPOE SERVERs in a network, users may receive multiple PADO echoes after they transmit PADI, and they will select one as server (the one that responds first). If a network has illegal PPPOE SERVER, it will fail the authentication of users, even a great deal of usernames and passwords are stolen. Once a user passes DISCOVERY stage, it will be authenticated on username and password; if it is of PAP authentication, the username and password are easy to be decrypted.
Solution: Locate the user according to the alarm and close PPPOE service.
Moreover, the MAC of illegal PPPOE server in the alarm is the one of MA5200F itself, which means that the packets transmitted by itself to detect illegal PPPOE server have been received by itself, indicating a loop in L2 network. At this point, check the L2 network and remove the loop.